klubnl.pl

RSDN stations are active again

After a long period of inactivity the RSDN stations are active again. Right now (12 october 2021) three frequencies are active: 11.9kHz, 12.65kHz, 14.88kHz.

This is a hyperbolic navigation system, which broadcasts a periodic carrier. More information is avaliable here: http://www.vlf.it/alphatrond/alpha.htm

For people interested in VLF this is a great test signal, whch can be used to check receiving equipment.

RSDN 2021

VLF grabbers reactivation at Warsaw / SQ5BPF

In 2019 i’ve written that the SQ5BPF grabbers will be temporarily offline and should return in winter 2019. Unfortunately this “moment” got extended to august 2021.

Now, finally, I’m trying to reactivate them, The VLF antenna has been installed again. For now I’ve activated the ZEVS 82Hz and VLF 8270Hz grabbers. Because of changes in vlfrx-tools noiseblanker from versions 0.6 to 0.9, i will be trying to find the parameters for best reception, so please stay tuned, the grabbers might not be operating at their best right now.

The rest of the grabbers will be activated shortly.

As before, i’m recording the while 0-24kHz bandwidth, and keeping the recordings for a few days. They can be provided to interested parties upon request (for scientific reasons etc).

Warsaw VLF receiver temporarily turned off

The VLF receiver in Warsaw (operated by Jacek/SQ5BPF) is currently turned off because the antenna had to be taken down.

This affects the VLF grabbers anf the stream on Nicholson’s page.

I hope to have the receiver running again in 1-2 months.

How Cave Communications works

Due to the ongoing (on 20 august 2019) rescue operation in the Wielka Śnieżna Cave in the Tatra mountains we decided to write about cave communications.

Rocks and soil attenuate radio signals well. Despite of this some means of communications in caves and mines are needed.

The attenuation rises with frequency. Normal VHF communications gear can’t be used, sometimes the distance can deteriorate to meters, depending on the geology and shape of tunnels. Of course cell phones are totally out of the question too. Shortwave radio behaves only a bit better.

Much larger distances can be achieved using low frequencies.

Continue reading “How Cave Communications works”

SAQ Alexanderson Day transmission on 20190630

A video of the SAQ Alexanderson Day transmission on 9:00 UTC 20190630.

Received at SQ5BPF QTH Warsaw/Poland KO02md.

E-field active antenna, vlfrx-tools and Spectrum Lab receiver

Transmission at 9:00 UTC:

Transmission at 12:00 UTC:

Record distance for a VLF transmission from an earth dipole antenna.

Recently we’ve done a successful transmission from an earth dipole on 8270 Hz.

This is the first amateur transmission on VLF from Poland which has been received in another country. This is also the record distance for a transmission using a ground dipole antenna – over 1330 km.

Link to Paul Nicholson’s post about it: https://klubnl.pl/rsgb_lf_group-archives/html/rsgb_lf_group/2019-03/msg00025.html

Link to Paul’s VLF milestones list: http://abelian.org/vlf/amateur-radio/

This is probably the first VLF signal which has been transmitted from Poland after World War II. We are not aware of any military or other transmissions. Before the war we had the Babice Transatlantic Radiostation (callsigns AXO/AXL/SPO/SPL), which was similar to Grimeton/SAQ.

VLF transmit tests from a ground dipole

Encouraged by our last experiments with ground dipoles we decided to do a transmit experiment with this antenna on VLF 8.270kHz, 36km (36000m) wavelength. Thanks to Fab LAB Trójmiasto we had a great location on the see on a cliff near the Baltic Sea in Gdynia. Our goals for this experiment were:

Try transmitting from a ground dipole on VLF
Assess the field strength near the sea
See if it is possible to reach greater distances with relatively simple equipment and low power.
Test a broadband transformer for VLF-LF-MF

Continue reading “VLF transmit tests from a ground dipole”

DK7FC ground dipole experiments on VLF

Stefan DK7FC did a succesful transmit experiment utilising a ground diole on VLF. This resulted in a really strong signal on our Warsaw grabber (over 900km distance):